The present invention relates to a plastic oil extraction technology, and more particularly to a method of converting waste plastics into hydrocarbon oil, and a system for carrying out the same.
The plastic oil extraction technology, or POET in short, has been used in processing solid wastes generated in urban areas and in industries. However, as noted in the research, it appears that there is still no practically applicable method and system of converting waste plastic into hydrocarbon oil. Most of the researchers in this particular field focus on the conversion of high polymer compositions into polymers of smaller molecules by utilizing thermal cracking of high temperature and high pressure, catalysts, while the operation platform used is either an oven type reactor or tubular type reactor. It is believed that the former reactor may be good for melting the solid plastics, but may not ensure the sufficient cracking, and discharge the residues efficiently, while the latter reactor is just opposite. The tubular reactor may efficiently discharge the residues of the cracking, but may not be suitable for processing directly the solid waste plastics.
The plastic oil extraction technology of prior art usually includes thermal cracking, catalytic cracking, and cooling. One of the prior methods and systems is disclosed in EP 0 607 862 A. In order to obtain purified hydrocarbon oil, it utilizes a neutralization tank, in which the low-boiling hydrocarbon oil is subjected to neutralization in a 20% sodium hydroxide aqueous solution, and an oligomerization tank, in which the cracking gas component is subjected to oligomerization in a 100% phosphoric acid in addition to the aforesaid thermal, catalytic cracking and cooling. The other prior method or system is disclosed in WO 00/64997 of the same inventor, Mr. Tianfu JIANG. In that system, a subsidiary reactor is used to have the residues of the main thermal cracking reactor undergone a secondary thermal cracking so as to ensure the waste plastics gasified, and a heavy oil separator is used to recycle the heavy oil back to the catalytic cracking reactor for further catalytic cracking.
However, the POET is aimed to process a mixture of hardly defined wastes plastics, containing many non-recyclable plastics, such as PP, PE, PVC, PET, PS, etc. in urban and industrial plastic wastes. Therefore, the conversion process from the solid wastes into a gaseous state can be hardly controlled. Thus, it creates lots of difficulties in the industrial application. This is probably the main reason why the plastic oil extraction technology has not been really put into practical use. The present invention is developed and perfected through many years of industrial research and practical testing. The present invention has solved the aforesaid difficulties, and thus can be readily adopted in the industrial application.
An object of the present system is to provide a method and system of converting the solid plastic wastes efficiently and thoroughly into pure and clean hydrocarbon oils of high calorie value up to about 11000 great calories per kilograms, and of a weight ratio of about 0.8. Such hydrocarbon oils can be used on any types of oil injection nozzle, and thus it can be widely used in the industry.
Another object of the present invention is to provide a system utilizing the combination of an oven reactor and a tubular reactor such that it can process various kinds of plastic wastes.
A still further object of the present invention is to provide a method and system of converting the solid plastic wastes into hydrocarbon oil without hazard hydrochloric acid.
In accordance with the present invention, a system of converting waste plastics into hydrocarbon oils comprises a thermal cracking reactor, into which solid waste plastics are fed and in which said waste plastics are cracked at a temperature in a range of 270-800xc2x0 C. to obtain a thermal cracking product of partly gaseous hydrocarbons, partly a mixture of liquid hydrocarbons and residues; a continuous thermal cracking and residual discharging portion connected to receive automatically the mixture of liquid hydrocarbons and residues from the thermal cracking reactor, in which the liquid hydrocarbons are gradually and cracked into gaseous hydrocarbons when passing through the thermal cracking and residual discharge portion, while the dry residues from the previous thermal cracking and residues newly generated from the farther thermal cracking are discharged at a residual discharge outlet of the thermal cracking and residue discharge portion; a [hydrochloride] hydrochloric acid removal portion connected to receive the gaseous hydrocarbons, respectively, from the thermal cracking reactor and from the continuous thermal cracking and residual discharge portion; a catalytic cracking reactor being connected to the hydrochloride removal portion in which the gaseous hydrocarbons from the hydrochloride removal portion is subjected to catalytic cracking with an acid catalyst; a cooling portion through which most of the gaseous hydrocarbons after the catalytic cracking are substantially converted into liquid hydrocarbons, and remaining non-convertible gaseous hydrocarbon substances are transported back to a burning chamber which compensates the heating of the thermal cracking reactor; and an pressurized activation reaction portion provided to receive the liquid hydrocarbons from the cooling portion to solidify few amount of sulfur nitrogen phosphorus contained in the liquid hydrocarbons so as to obtain purified hydrocarbon oils, thereby reducing the generation of SOx and NOx.
The thermal cracking and residual discharge portion consists of continuous thermal reacting tubes of parallel arrangement. A mixture of the melting waste plastics and other impurities, that is, liquid hydrocarbons and residues, is pushed forward by screw conveyors mounted inside the tubes, and thus passes through the thermal reacting tubes while the mixture is maintained at a high temperature sufficient to enable further gasification of the melting wastes plastics, or rather liquid hydrocarbons, to ensure the sufficient thermal cracking of the gaseous hydrocarbons.
The hydrochloride removal reaction of the present invention is to have the thermal cracking products, i.e., gaseous hydrochloric acid, in reaction with alkaline substances to replace the chlorine from hydrochloric acid contained in the thermal cracking products so as to obtain purified gaseous hydrocarbons. The hydrochloride removal reaction is at a high temperature. After the reaction, the gaseous hydrocarbons are hydrochloric acid free.
The cooling portion of the present invention consists of three stages of cooling, whereby gaseous alkene of large molecules will be substantially converted into gaseous alkene of small molecules, such as eight to twenty carbon atoms, and eventually become liquid hydrocarbons, leaving only few non-convertible gaseous hydrocarbon substance, that is, non-convertible at room temperature and pressure. Such non-convertible gaseous hydrocarbon substances will be sent back to the burning chamber for the thermal cracking reactor to compensate the heating supply for the thermal cracking reaction.